In magnetic levitation railways, ground coils are continuously mounted along a guideway thereof to levitate, guide and propel a vehicle. The ground coils each having a predetermined length corresponding to a pole pitch of a superconducting magnet of the vehicle are continuously disposed at a predetermined pitch (a longitudinal distance between centers of adjacent superconducting coils in the same superconducting magnet).
As to the ground coils for magnetic levitation railway, there are conventionally known only inventions relating to coil devices produced using a thermosetting resin by a sheet molding compound (SMC) method or a reaction injection molding (RIM) method, and processes for production thereof.
For example, FIG. 1 is a cross-sectional view showing a conventional ground coil device for magnetic levitation railway, and FIG. 2 is a front view as viewed from the direction of the line A-A of FIG. 1 (for example, refer to JP 3301892).
In FIGS. 1 and 2, a concrete track 1 having a U-shaped section is constituted of a side wall 1a and a bottom wall 1b. A propulsion coil 2 for generating a propulsion force of a vehicle (not shown) is affixed to the side wall 1a, and a levitation coil 3 for levitating and guiding the vehicle is also affixed to the side wall 1a at a position nearer to a center of the concrete track 1 than that of the propulsion coil 2. Meanwhile, reference numeral 4 denotes a tightening means composed of a fixing bolt and a washer for affixing the levitation coil 3 to the side wall 1a. 
A conductor of the propulsion coil 2 is covered with a sheath made of an epoxy resin, whereas an outer periphery of a conductor 3a of the levitation coil 3 is covered with a sheath made of SMC. Meanwhile, the SMC is obtained, for example, by compounding a thermosetting polyester resin and a glass fiber base material and forming the resultant mixture into a sheet having a thickness of about 2 mm. The glass fibers used in the SMC generally have such a composition that those fibers having a length of 3 to 6 mm are contained therein in an amount of about 30% by mass, in view of a good fluidity thereof within a mold upon heat- and pressure-molding. However, in the present invention, in order to avoid occurrence of such portions where a density of the glass fibers is lacking and fluctuation of mechanical strength in the obtained products due to undesirable flow of the resin upon molding, continuous glass fibers in the form of a vortex are used in the SMC.
Also, in JP 3121718, using an insulting sheath made of an epoxy resin, a ground coil device is molded by a cast molding method. In the invention described in JP 3121718, in order to avoid induction of eddy current in a metal bush and occurrence of peeling between the metal bush and the epoxy resin and eliminate a step for removal of burrs of the epoxy resin, a conductive coating film is formed on an outer peripheral surface of the metal bush, or a shape of the metal bush is variously designed.
In addition, in JP 10-315267A, a coil device is molded by a reaction injection molding method using a norbornene-based polymer as a material of an insulating sheath thereof. In the invention described in JP 10-315267A, in order to avoid displacement of winding coils inserted into a metal mold from predetermined positions in the metal mold, a previously shaped reinforcing mat is placed within the metal mold.
As described above, with respect to the ground coil devices for magnetic levitation railway, there have been conventionally proposed various inventions relating to processes for manufacturing the devices by compression molding, cast molding or reaction injection molding of thermosetting resins.
However, upon molding the thermosetting resins, irrespective of the molding method used therefor, a very long molding cycle time (SMC: 30 min or more; RIM: 1 h or more) as well as post-treatments such as removal of burrs are inevitably required, resulting in poor productivity. In addition, when subjecting the SMC to compression molding, coarse and dense distribution of the glass fibers in the SMC tends to occur due to flowing of the material, thereby causing such a problem that the obtained molded product tends to be fluctuated in strength depending upon positions thereof. On the other hand, in the RIM, it is required to insert a previously shaped mat into a metal mold, resulting in still poorer productivity.
Further, the glass fibers are hardly penetrated into thin-wall rib portions, resulting in low reliability in strength of such a rib structure. Therefore, in order to ensure a sufficient strength required for the coil devices, it is required to increase a thickness of the resin portion, so that the resultant devices inevitably suffer from increase in weight.
Furthermore, the thermosetting resins inherently have a poor recyclability.